The invention relates to a piston for a compressor with a piston stem for guiding the piston and a piston engagement section where a drive force can be applied to the piston to move the piston in an axial direction and a piston stem for transferring the drive force to the piston head.
In air-conditioning systems for motor vehicles, axial piston compressors are used to compress coolants, wherein so-called swash plates serve as force transmission elements between the drive shaft and the pistons. The compression generally takes place through periodic movement of the pistons in the cylinders, whereby the coolant is sucked in, compressed and expelled. The axial movement of the piston is generated by the swash plate, which is connected to the rotating shaft of the compressor and encloses an angle between approximately 60° and 90° with the axis of rotation. The rotational movement results in a reciprocating movement at the pistons. A shoulder of each piston engages the swash plate, which thus transmits the reciprocating movement to the piston and converts the shaft rotation to an oscillating movement of the piston. Up until now, pistons are assembled from two parts in order to form a hollow configuration. It is necessary to guide the pistons and provide for a small oscillating mass. A quantity of lubricant, which is introduced into the coolant, is used to lubricate the pistons and the drive shaft of the compressor. With coolants such as R134a, the lubricant is circulated continuously with the coolant. With coolants such as CO2, a lubricant precipitator separates the lubricant from the coolant downstream of the compressor. The lubricant is then again returned to the compressor for lubrication.
In DE 197 46 896 A1, a compressor with pistons for compressing a gas is described in which the rotation of a drive shaft can be converted into linear reciprocal movement of the piston by means of drive elements such as swash plates. The object here is to minimize the weight of the pistons by reducing the material without adversely affecting the function of the sealing the compression chamber and the compression of the gas in the chamber. For this purpose, the piston has, in the region of the compression chamber, two areas, which are continuously in contact with the cylinder cavity and thus seal the chamber. Furthermore, the piston has a space, which opens to the cylinder cavity of the piston, the space being located between the second face and the apron, which transmits the movement of the swash plate to the pistons. However, when transverse forces occur, the piston is not guided satisfactorily in the cylinder cavity.
DE 197 54 028 A1 discloses a piston for a compressor with the same function as described mentioned above which is distinguished by two radial recesses which are offset by an angle of 180° between the sealing face of the sealing chamber and the apron in the circumferential face in order to reduce its weight. When there are transverse forces in the cylinder cavity, it is possible to guide the piston as a function of the direction. However, the loads on the cylinder cavity walls and piston are not homogeneously distributed, as a result of which increased wear can occur. Furthermore, the piston has, for fabrication reasons, a face extending over the entire cylinder cavity between the two recesses, which is without function and thus only increases the weight.
U.S. Pat No. 5,630,353 describes a piston corresponding to the above function, which piston is distinguished by ribs arranged in a star shape underneath the piston head and the necessary seal of the compression chamber in order to reduce the weight. These ribs are radially deformed and accordingly when transverse forces occur they do not provide for guidance over the complete circumference of the cylinder.
EP 1 022 463 A2 describes a piston according to the above-mentioned function which is manufactured from two parts made of different materials. Here, the apron is composed of metal and is joined, in a shaping process, to the cylindrical body, which closes off the sealing chamber. The body finally receives its shapes in this method. The connection of the two bodies takes place by means of a small hook on the apron, which is surrounded by the material of the cylindrical body. A disadvantage of this solution is the fact that the entire axial tensile force, which acts on the piston, has to be transmitted by the connection between the apron and cylindrical body.
EP 0 945 615 A2 also discloses a compressor piston which has a piston head for compressing a medium, a piston stem for axially guiding the piston in a housing and a force application section for applying an external drive force to the piston. The piston head, piston stem and force application section are arranged one behind the other in the direction of the piston, the piston stem having a strut which is oriented in parallel with the piston axis and has a W-shaped cross section. The shaping which is indicated here permits a reduction in weight even when a metallic material is used.
U.S. Pat. No. 5,941,161 finally also discloses a piston for a compressor which has a piston head for compressing a medium, a piston stem for axially guiding the piston in a housing and an engagement section for applying an external drive force to the piston. The piston head, piston stem and engagement section are arranged one behind the other in the direction of the piston axis, the piston stem having a solid strut, which is oriented in parallel with the piston axis. U.S. Pat. No. 5,941,161 discloses various shapes of such a strut which can be implemented with an aluminum alloy.
It is the object of the invention to provide a piston, which has a particularly low weight, is easy to manufacture and permits a particularly simple design and operation of the compressor.